Field of the Invention
Embodiments of the present invention relate generally to an electron gun supporting member and an electron gun apparatus, and more specifically, to an electron gun apparatus used as a beam source for a charged particle beam writing apparatus, for example.
Description of Related Art
An electron gun being a beam source is used in an electron beam apparatus, such as an electron beam writing or “drawing” apparatus and an electron microscope. In terms of electron beam writing, for example, it has excellent intrinsic resolution, and is used for producing a highly accurate master pattern.
The lithography technique that advances miniaturization of semiconductor devices is extremely important as a unique process whereby patterns are formed in semiconductor manufacturing. In recent years, with high integration of LSI, the line width (critical dimension) required for semiconductor device circuits is decreasing year by year. For forming a desired circuit pattern on such semiconductor devices, a master or “original” pattern (also called a mask or a reticle) of high accuracy is needed. The electron beam writing apparatus is used in production of such a high-accuracy master pattern.
FIG. 9 is a conceptual diagram explaining operations of a variable shaped electron beam writing or “drawing” apparatus. The variable shaped electron beam (EB) writing apparatus operates as described below. A first aperture plate 410 has a quadrangular aperture 411 for shaping an electron beam 330. A second aperture plate 420 has a variable shape aperture 421 for shaping the electron beam 330 having passed through the aperture 411 of the first aperture plate 410 into a desired quadrangular shape. The electron beam 330 emitted from a charged particle source 430 and having passed through the aperture 411 is deflected by a deflector to pass through a part of the variable shape aperture 421 of the second aperture plate 420, and thereby to irradiate a target object or “sample” 340 placed on a stage which continuously moves in one predetermined direction (e.g., x direction) during writing. In other words, a quadrangular shape that can pass through both the aperture 411 of the first aperture plate 410 and the variable shape aperture 421 of the second aperture plate 420 is used for pattern writing in a writing region of the target object 340 on the stage continuously moving in the x direction. This method of forming a given shape by letting beams pass through both the aperture 411 of the first aperture plate 410 and the variable shape aperture 421 of the second aperture plate 420 is referred to as a variable shaped beam (VSB) system.
Electron beams used for the electron beam writing apparatus are accelerated by a high voltage of several 10 kV, for example. In the electron gun apparatus, the electrode of such a high voltage is supported by a supporting member. However, there is a problem in that a creeping discharge may occur on the surface of the supporting member. If a creeping discharge occurs, the acceleration voltage of an electron beam is changed, which causes beam current fluctuation. Consequently, the writing accuracy of patterns to be written is degraded. Although conditioning is conventionally performed for a sufficient time period at the OFF line to improve the breakdown voltage when an electron gun is fabricated, the breakdown voltage characteristic is decreased due to subsequent use. Besides, there is disclosed a technique in which a groove is formed in a high voltage insulating glass in relation to discharge suppression of an electron gun (e.g., refer to Japanese Patent Application Laid-open (JP-A) No. 2002-313269).